SECTION B. SIPHONIDA.
Family 7. Chronicle.. Shell inequivalve; adductor impressions large; Mantle mar gins united; siphonal orifices small. See CIIAMA.
Family 8. ilippuritidee. Shell inequivalve, unsymmetrical, thick. See IhrrunrrEs and RADIOLITES.
Family 9. Tridoenidm (q.v.). Shell equivalve, large, and very beautiful; mantle margins extensively united; siphonal orifices surrounded by a thickened border. See CLAM, BEAR'S PAW.
Family 10. Cardiode. Shell equivalve, heart-shaped, with radiating ribs; mantle open in front; siphons usually short. See COCKLE.
Family 11. Luciaide. Fossils mostly found in secondary, tertiary, and recent formations, but some are Devonian and carboniferous, See LUC1NA.
Family 12. Cycladide. Shell sub-orbicular; mantle open in front; at single siphon, or two more or less united. Cyclas and cyrena, are the two most important members, and date from the commencement of the cretaceous period to present time. They inhabit fresh water.
Family 13. Cyprinide. (There is also a genus of fishes of this name.) Shell equi valved; mantle margins united b hind by- a curtain. The animals comprising this group are represented by Cyprina and Astarte. The latter has sometimes been assigned
to the rank of a distinct family, Astartid. bee ASTARTE.
Family 14. Yencride (q.v.).
Family 15. Mactride. Sec MACTRA.
Family 16. Tcllinithe (q.v.).
Family 17. &Weide. See SOLEN.
Family 18. Ifgacide. The more important genera are mya, Meas. and pa nopmra (q.v.).
Family 19. Anatinide. Mantles more or less united; siphons long, more or less united. This family has considerable paleontological importance, numerous in paleo zoic, and reaching a great development in secondary formations.
Family 20. Gastrochenider. Mantle margins thick in front; siphons long and united; burrowing in mud, and predaceons'upon oysters and other mollusks. burrowing holes through their shells. Range from oolite to the present time. See ASPERGILLUM, GAS TROCHAINA, and CLAVAGELLA.
Family 21. Pholadidie. Many fossil species are found in Jurassic rocks. The living genus, xylophaga, includes the teredo (q.v.). See PirokAs.
Encephalic division of mollusca, or cephalophora.